In many industries where complex machinery is employed, it is common to form housings for enclosing a multitude of components, such as a gear box housing, in two parts which are originally formed as castings and then are machined to provide the desired internal configuration and a peripheral parallel mating surface on each component which are traversed by peripherally spaced bolt holes to receive bolts which effect the sealed securement of the two housing parts.
This technique is employed to manufacture gear box housings for aircraft jet engines with the exception that the castings are formed from a magnesium or aluminum alloy or other suitable material due to the necessity of minimizing the weight of the gear box housing. The shafts and gears mounted in such housing are normally lubricated by a continuous flow of lubricating oil. The slightest leakage between the peripheral mating faces of the two gear box housings not only permits the oil to leak out but may also permit external contaminants such as water to gain entrance to the interior of the gear box housing. More importantly, the gear box housing must maintain its sealed relationship through a wide range of temperatures. Temperatures of minus 50.degree. F. are often encountered by jet aircraft flying at altitudes on the order of 30,000 feet. On the other hand, when the aircraft is on the ground and the ground temperature is 100.degree. F., the temperature of the housing and its contained components may reach the level of 400.degree. F. These extreme reversals of temperature, which occur every time the jet aircraft takes off or lands, impose substantial stresses on the gear box housing. Additionally, these stresses are amplified by stresses derived from the gear shafts which are mounted in bearings supported by machined bores within the gear box housing.
It is therefore fairly common for the peripheral mating surfaces of one or both of the gear box housings to warp and depart from their original condition of exact parallelism with each other, thus permitting leakage to develop. Furthermore, lubricating oils are subject to breakdown by the temperature cycles, producing compounds which attack the magnesium alloy from which the gear box castings are formed. These contaminants can result in corrosion of sealing surfaces within the casting, thus permitting undesired leakage of the internal hydraulic system. Leakage can also be caused by external corrosion as a result of exposure to the elements. Lastly, breakage of protruding beating hubs integrally formed on the wall of the casting is not uncommon.
From the foregoing, it will be apparent that gear box housings for jet aircraft have a limited life, yet these housings are individually very expensive to manufacture due to their complexity. As illustrated in FIGS. 1A and 1B of the drawings, each half of the housing comprises a complex casting which is subjected to a multitude of machining operations to produce the various bearing bores identified in such figures. The total cost of a single front or rear housing is on the order of $20,000. There is a need, therefore, for a repair technique to restore the housing to its original machined condition without in any manner decreasing the strength or serviceability of the housing and accomplishing such repair for a figure on the order of $5,000 or less to provide a substantial economic incentive for repairing such complex metallic components rather than scrapping them.